Transmission of COVID-19

A person can become infected through the inhalation of respiratory droplets from an infected individual (including aerosols generated through sneezing, coughing, speaking, singing, or breathing) or through direct contact with infected droplets through the eyes, mouth, or nose.

Transmissibility, incubation period, and infectivity varies depending on the virus variants and the individual immunity.

The incubation period of COVID-19 ranges from two to 14 days, with an average of five to six days for earlier strains. Some variants, like Omicron, have a shorter incubation period (three to four days) [30].

An individual is infectious if carrying and shedding viable infectious SARS-CoV-2, regardless of whether they have symptoms [31]. The infectivity period is the period during which people can transmit SARS-CoV-2 to others. An infected person can transmit the virus up to two days before they experience symptoms, indicating that the pre-symptomatic phase of COVID-19 is highly infectious [32]. The infectivity period may also be affected by disease severity, pre-existing immunity through vaccination, or prior infection [33-35]. The presence of SARS-CoV-2-RNA detected through RT-PCR in a patient (i.e. viral RNA shedding) does not necessarily indicate the presence of infectious SARS-CoV-2 and viable viral shedding.